Vehicle air supply systems are provided for supplying compressed air to pneumatic systems such as pneumatic brakes, pneumatic suspension systems and pneumatic assistance devices in the vehicle. A compressor of a vehicle air supply system generally comprises a compressor block (cylinder block) with an air channel system and a cylinder piston unit. The air channel system provides an inlet air passage, a discharge air passage, at least one coolant channel, and, preferably, a cylinder bore.
Air is sucked through an inlet, for example an inlet flange and the inlet air passage, to a cylinder inlet of the cylinder piston unit in which the air is compressed. The compressed air is then delivered from a cylinder outlet through the discharge air passage to an outlet, for example an outlet flange. The compressed air can then be delivered to a dryer unit for filtering and drying.
Compressors used in vehicles often comprise active cooling systems having coolant channels that can be supplied with a coolant liquid, such as water, in order to cool the compressed air, since the temperature of the air is increased during the compression process. This temperature increase results in an increase in the total temperature of all compressor components and can reduce compressor lifespan.
The cylinder block housing the cylinder piston unit is therefore designed with an eye toward improving heat transfer from the discharge air passage to the coolant channel. The discharge air passage and the coolant channel are located near each other and separated by a wall. One option to improve heat transfer is to guide the discharge air passage and the coolant channel over a long distance and close to each other, thereby enlarging the wall area between these channels. However, the length of the discharge air passage is limited by design constraints, and the flow resistance increases with a smaller cross-sectional area of the discharge air passage. Thus, heat transfer is limited.
To improve heat transfer, it is known to enlarge the surface area of the discharge area. This can be accomplished by providing the long discharge passage or by providing a structure in the surface of the walls of the wide first area of the discharge passage. This structure can comprise protrusions extending into the first area. However, with such constructions, cooling efficiency is limited, and cooling the cylinder block remains a problem.
Further compressor systems are used in cooling devices to compress a refrigerant gas and to deliver the compressed gas—see, e.g., U.S. Pat. Nos. 5,775,885 and 6,568,920. EP 1 288 499 A2 describes another known compressor system.